The present invention relates to an imaging optical system which is usable, for example, for projecting an image of an object onto another object, as in semiconductor manufacturing apparatus.
U.S. Pat. Nos. 3,748,015, 3,821,763 and 4,097,125 disclose a so-called off-axis imaging optical system, in which the aberration is corrected at a point or a zone which is away from the optical axis thereof rather than on the optical axis thereof. U.S. Pat. No. 4,293,186 discloses an imaging optical system wherein two off-axis imaging optical systems are coaxially arranged. Further, USSR Patent No. 126,911 discloses an imaging optical system wherein an on-axis imaging optical system is eccentrically arranged with respect to an off-axis imaging optical system.